Question: What number makes this equation true? $230 + $
$230 +{{?}}= 378$ ${230}$ ${378}$ $+?$ Let's start by adding hundreds to ${230}$ until we get as close to ${378}$ as possible without going over ${378}$. $\begin{aligned} {230} +100}=330 \end{aligned}$ If we add $1 \text{ hundred}}$, or $1 00}$, we reach $330$. We cannot add any more hundreds without going over ${378}$. ${230}$ ${378}$ ${330}$ $+100$ Next, let's add tens to $330$ until we get as close to ${378}$ as possible without going over ${378}$. $\begin{aligned} 330 +{10}=340\\\\ {340} +{10}= 350\\\\ {350} +{10}= 360\\\\ {360} +{10}= 370 \end{aligned}$ If we add ${4 \text{ tens}}$, or ${40}$, we reach $370$. We cannot add any more tens without going over ${378}$. ${230}$ ${378}$ ${330}$ ${370}$ $+100$ $+40$ Finally, how many ones should we add to $370$ to get to ${378}?$ $370 +{8}={378}$ ${230}$ ${378}$ ${330}$ ${370}$ $+100$ $+40$ $+8$ We added $1 \text{ hundred}}$, ${4 \text{ tens}}$, and ${8\text{ ones}}$ to ${230}$ to get to ${378}$. $1 00}+{4 0}+{8}={148}$ ${230}$ ${378}$ ${330}$ ${370}$ $+100$ $+40$ $+8$ $+148$ $230 +{148}= 378$